4X games are noted for their deep, complex gameplay. Emphasis is placed upon economic and technological development, as well as a range of non-military routes to supremacy. Games can take a long time to complete since the amount of micromanagement needed to sustain an empire scales as the empire grows. 4X games are sometimes criticized for becoming tedious for these reasons, and several games have attempted to address these concerns by limiting micromanagement, with varying degrees of success.

The earliest 4X games borrowed ideas from board games and 1970s text-based computer games. The first 4X games were turn-based, but real-time 4X games are not uncommon. Many 4X games were published in the mid-1990s, but were later outsold by other types of strategy games. Sid Meier's Civilization is an important example from this formative era, and popularized the level of detail that later became a staple of the genre. In the new millennium, several 4X releases have become critically and commercially successful.

4X games such as Master of Orion II let empires explore the map, expanding by founding new colonies and exploiting their resources. The game can be won either by becoming an elected leader of the galaxy or by exterminating all opponents.

The term "4X" originates from a 1993 preview of Master of Orion in Computer Gaming World by Alan Emrich, in which he rated the game "XXXX" as a pun on the XXX rating for pornography. The four Xs were an abbreviation for "EXplore, EXpand, EXploit and EXterminate".[1] Other game commentators adopted the "4X" label to describe a game genre with specific gameplay conventions:[2]

Expand means players claim new territory by creating new settlements, or sometimes by extending the influence of existing settlements.

Exploit means players gather and use resources in areas they control, and improve the efficiency of that usage.

Exterminate means attacking and eliminating rival players. Since in some games all territory is eventually claimed, eliminating a rival's presence may be the only way to achieve further expansion.

These four elements of gameplay have been described as the four phases of a 4X game session.[3] These phases often overlap with each other and vary in length depending on the game design. For example, the Space Empires series and Galactic Civilizations II: Dark Avatar have a long expansion phase, because players must make large investments in research to explore and expand into every area.[4]

While many strategy games arguably contain a similar "explore, expand, exploit, exterminate" cycle,[5] game journalists, developers and enthusiasts generally apply "4X" to a more specific class of games,[5] and contrast 4X games with other strategy games such as Command & Conquer.[6][7] Hence, writers have tried to show how 4X games are defined by more than just having each of the four Xs. Gaming sites have stated that 4X games are distinguished by their greater complexity and scale,[8] and their intricate use of diplomacy beyond the standard "friend or foe" seen in other strategy games.[9] Reviewers have also stated that 4X games feature a range of diplomatic options,[10] and that they are well known for their large detailed empires and complex gameplay.[11][12] In particular, 4X games offer detailed control over an empire's economy, while other strategy games simplify this in favor of combat-focused gameplay.[8]

4X games are a subgenre of strategy games,[2] and include both turn-based and real-time strategy titles.[13][14] The gameplay involves building an empire,[15] which takes place in a setting such as Earth,[16] a fantasy world, or in space.[3] Each player takes control of a different civilization or race with unique characteristics and strengths. Most 4X games represent these racial differences with a collection of economic and military bonuses.

One part of Freeciv '​s technology tree. Note the complex dependencies between technologies.

4X games typically feature a technology tree, which represents a series of advancements that players can unlock to gain new units, buildings, and other capabilities. Technology trees in 4X games are typically larger than in other strategy games, featuring a larger selection of choices.[5][17] Empires must generate research resources and invest them in new technology.[18] In 4X games, the main prerequisite for researching an advanced technology is knowledge of earlier technology.[6] This is in contrast to non-4X real-time strategy games, where technological progress is achieved by building structures that grant access to more advanced structures and units.[19]

Research is important in 4X games because technological progress is an engine for conquest.[20] Battles are often won by superior military technology or greater numbers, with battle tactics playing a smaller part.[21] In contrast, military upgrades in non-4X games are sometimes small enough that technologically basic units remain important throughout the game.[22]

Combat is an important part of 4X gameplay, because 4X games allow a player to win by exterminating all rival players, or by conquering a threshold amount of the game's universe.[23] Some 4X games, such as Galactic Civilizations, resolve battles automatically, whenever two units from warring sides meet.[24] This is in contrast to other 4X games, such as Master of Orion, that allow players to manage battles on a tactical battle screen.[24][25] Even in 4X games with more detailed control over battles, victory is usually determined by superior numbers and technology, with battle tactics playing a smaller part.[21] 4X games differ from other combat-focused strategy games by putting more emphasis on research and economics.[1][8] Researching new technology will grant access to new combat units. Some 4X games even allow players to research different unit components. This is more typical of space 4X games, where players may assemble a ship from a variety of engines, shields, and weaponry.[24]

In 4X games, such as the pictured Sins of a Solar Empire, competing players may negotiate treaties with each other.

4X games allow rival players to engage in diplomacy.[10] While some strategy games may offer shared victory and team play, diplomatic relations tend to be restricted to a binary choice between an ally or enemy. 4X games often allow more complex diplomatic relations between competitors who are not on the same team.[9] Aside from making allies and enemies, players are also able to trade resources and information with rivals.[14]

In addition to victory through conquest, 4X games often offer peaceful victory conditions/goals that involve no extermination of rival players (although war may be still be a necessary by-product of reaching said goal).[8] For example, some 4X games offer victory to a player who achieves a certain score or the highest score after a certain number of turns.[26] Many 4X games award victory to the first player to master an advanced technology, accumulate a large amount of culture, or complete an awe-inspiring achievement.[24] Several 4X games award "diplomatic victory" to anyone who can win an election decided by their rival players,[27] or maintain peace for a specified number of turns.[26]

4X games are known for their complex gameplay and strategic depth.[28] Gameplay usually takes priority over polished graphics.[17][29] Whereas other strategy games focus on combat, 4X games also offer more detailed control over diplomacy, economics, and research;[1][8] creating opportunities for diverse strategies.[30] This also challenges the player to manage several strategies simultaneously, and plan for long-term objectives.[31]

To experience a detailed model of a large empire, 4X games are designed with a complex set of game rules.[12] For example, the player's productivity may be limited by pollution.[32][33] Players may need to balance a budget, such as managing debt,[34] or paying down maintenance costs.[35] 4X games often model political challenges such as civil disorder,[23][32] or a senate that can oust the player's political party or force them to make peace.[32][36]

FreeCol is typical of 4X games where there is a separate interface for managing each settlement.

Such complexity requires players to manage a larger amount of information than other strategy games.[37] Game designers often organize empire management into different interface screens and modes,[8] such as a separate screen for diplomacy,[38] managing individual settlements, and managing battle tactics.[24][25] Sometimes systems are intricate enough to resemble a minigame.[31][39] This is in contrast to most real-time strategy games. Dune II, which arguably established the conventions for the real-time strategy genre, was fundamentally designed to be a "flat interface", with no additional screens.[19]

Since 4X games involve managing a large, detailed empire, game sessions usually last longer than other strategy games.[8] Game sessions may require several hours of play-time, which can be particularly problematic for multiplayer matches.[40] For example, a small-scale game in Sins of a Solar Empire can last for over 12 hours.[12] However, fans of the genre sometimes expect and embrace these long game sessions;[41] Emrich wrote that "when the various parts are properly designed, other X's seem to follow. Words like EXcite, EXperiment and EXcuses (to one's significant others)".[1] Turn-based 4X games typically divide these sessions into hundreds of turns of gameplay.[31][42]

Because of repetitive actions and long-playing times, 4X games have been criticized for excessive micromanagement. In early stages of a game this is usually not a problem, but later in a game directing an empire's numerous settlements can demand several minutes to play a single turn. This increases playing-times, which are a particular burden in multiplayer games.[40] 4X games began to offer AIgovernors that automate the micromanagement of a colony's build orders, but players criticized these governors for making bad decisions. In response, developers have tried other approaches to reduce micromanagement,[43] and some approaches have been more well received than others. Commentators generally agree that Galactic Civilizations succeeds, which GamingNexus.com attributes to the game's use of programmable governors.[44]Sins of a Solar Empire was designed to reduce the incentives for micromanagement,[45] and reviewers found that the game's interface made empire management more elegant.[37][46] On the other hand, Master of Orion III reduced micromanagement by limiting complete player control over their empire.[47][48]

In 1991, two highly influential space games were released. VGA Planets was released for the PC, while Spaceward Ho! was released on the Macintosh. Although 4X space games were ultimately more influenced by the complexity of VGA Planets, Spaceward Ho! earned praise for its relatively simple yet challenging game design.[52]Spaceward Ho! is notable for its similarity to the 1993 game Master of Orion,[1][53] with its simple yet deep gameplay.[25]Master of Orion also drew upon earlier 4X games such as Reach for the Stars,[1][54] and is considered a classic game that set a new standard for the genre.[25][40] In a preview of Master of Orion, Emrich coined the term "XXXX" to describe the emerging genre.[1] Eventually, the "4X" label was adopted by the game industry, and is now applied to several earlier game releases.[55]

By the late 1990s, real-time strategy games began outselling turn-based games.[60] As they surged in popularity, major 4X developers fell into difficulties. Sid Meier's Firaxis Games released Sid Meier's Alpha Centauri in 1999 to critical acclaim, but the game fell short of commercial expectations.[61]Civilization III encountered development problems followed by a rushed release in 2001.[62] Despite the excitement over Master of Orion III, its release in 2003 was met with criticism for its lack of player control, poor interface, and weak AI.[48]Game publishers eventually became risk-averse to financing the development of 4X games.[11]

Eventually real-time 4X games were released, such as Imperium Galactica in 1997,[13]Starships Unlimited in 2001, [14] and Sword of the Stars in 2006, featuring a combination of turn-based strategy and real-time tactical combat. The blend of 4X and real-time strategy gameplay led Ironclad Games to market their 2008 release Sins of a Solar Empire as a "RT4X" game.[63] This combination of features earned the game a mention as one of the top games from 2008, including GameSpot's award for best strategy game, and IGN's award for best PC game.[64]

Cross-fertilization between board games and video games continued. For example, some aspects of Master of Orion III were drawn from the board game Twilight Imperium.[65] Even Sins of a Solar Empire was inspired by the idea of adapting the board game Buck Rogers Battle for the 25th Century into a real-time video game.[66] Going in the opposite direction, Eagle Games made a board game adaptation of Sid Meier's Civilization in 2002.[67]